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0 pointsmumblemumble6y ago0 comments

Ideally, a good compiler that understands FP will, behind the scenes, detect when it's safe to mutate the old data rather than creating a copy. That's a big part of why Haskell manages to be neck-and-neck with C despite being functionally pure.

Where it gets tricky is in an environment like the JVM where programming in that style was not anticipated, and introducing any optimizations along these lines for the benefit of the proverbial Scala fans needs to be balanced against the obligation not to adversely impact idiomatic Java code.

That said, even without that, it's not necessarily crazy. It's just a value call: Do you believe that more functional code is easier to maintain, and perhaps value that above raw performance? I'm old enough to remember similar debates about how object-oriented C++ code should be, and to have at least encountered Usenet posts from similar debates about how structured C code should be. I don't bring this up by way of trying to weasel in some "historical inevitability" argument - these are legitimate debates, and there are still problem domains where coding guidelines may discourage, or even prohibit, certain structured programming practices. For very good reasons.

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12 comments · 3 top-level

nonsense12346y ago· 5 in thread

Haskell is only close to C in extremely rare cases or when using unsafe features and the FFI.

the_af6y ago

Would you say idiomatic Haskell is faster or slower than idiomatic use of Java and the JVM? I'm interested in actual experience and preferably benchmarks of real cases, no thought experiments please :)

(If this sounds harsh, it's not my intention. In another HN thread I had someone "explain" to me how Java and Java's OOP is "not suitable for business software development". If this seems like a bizarre statement which disregards more than a decade of business software development -- this is why I ask for actual experience and not opinions or "I think this can't be right").

bcrosby956y ago

Lots of people hate Java. It's unsuitable for those people.

There are certain things you might have trouble getting Java to perform, such as strict latency requirements. Another language might be more suitable for that. But that generally doesn't describe business software.

Desktop software is somewhere you probably don't want to use Java. Although if it's business desktop software, it might be a good fit since it can be cross platform (but ugly - but if it's business, it might not matter). We've built several desktop apps for warehouse computers in Java.

Getting the JVM on a machine may or may not be a hurdle. This is one of many reasons why Go is getting popular - you can just build a binary.

The positive of Java is that if you want to do something in it, someone else has probably tried. It has several large organizations backing professional quality libraries and frameworks that have had a ton of resources poured into them. It's easy to build on the shoulders of giants while relying on 3rd party libraries that don't have a bus factor of 1 - this is rare in many other languages.

If you want stability and well trodden paths, it's hard to go wrong with Java. We've had projects that continued to just work from Java 1.4 to Java 8 - a span of almost 15 years without ever having to touch the code. Java 9 was a bit of a hurdle because of project Jigsaw.

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igouy6y ago

Which person's idea of idiomatic ?

"One can, with sufficient effort, essentially write C code in Haskell using various unsafe primitives. We would argue that this is not true to the spirit and goals of Haskell, and we have attempted in this paper to remain within the space of reasonably idiomatic Haskell. However, we have made abundant use of strictness annotations, explicit strictness, and unboxed vectors. We have, more controversially perhaps, used unsafe array subscripting in places. Are our choices reasonable?"

http://www.leafpetersen.com/leaf/publications/ifl2013/haskel...

Programs for the n-body and spectral-norm procedural benchmarks game tasks, perform kind-of the same in Haskell and Java

https://benchmarksgame-team.pages.debian.net/benchmarksgame/...

mrkeen6y ago

These benchmarks seem pretty good. Filterable by language, etc.

https://www.techempower.com/benchmarks/

The source code is published too (https://github.com/TechEmpower/FrameworkBenchmarks)

wtetzner6y ago

“Unsuitable” doesn’t mean it can’t be done. Having written a lot of business software in Java, I actually agree it’s unsuitable. The only way I’ve been able to make it bearable is by using Lombok and pcollections.

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chrisseaton6y ago· 3 in thread

> That's a big part of why Haskell manages to be neck-and-neck with C despite being functionally pure.

Come on... that's not what you typically get with Haskell, is it.

nicoburns6y ago

Rust gives you FP-style without loads of copies and C-like performance. Immutable data-structures aren't idiomatic, but it's ownership gives you most of the same benefits.

zozbot2346y ago

The nice thing about Rust is that it gives you the main benefits of FP even when you're not programming in "FP style". The Rust "sharing xor mutability" default model provides underlying semantics and ease of analysis that's quite comparable to what you get with a pure-functional language. Of course extended mutability as with Cell<>, RefCell<> etc. undermines this, but these are only used when necessary.

entha_saava6y ago

And many string types, like Haskell /s

entha_saava6y ago· 1 in thread

> Ideally, a good compiler that understands FP will, behind the scenes, detect when it's safe to mutate the old data rather than creating a copy. That's a big part of why Haskell manages to be neck-and-neck with C despite being functionally pure.

Not talking against Haskell or FP; The disadvantage is being hard to reason about performance. Ensuring compiler will optimize something will take more cognitive load than simply writing straightforward code.

Imagine having a map() method on an array that produces another array. In a long chained pipeline of such things, compiler may be able to elide extra allocations and generate asm very near to handwritten for loops. But the abstraction breaks when the method does I/O or has side effects - you can't reorder anything in order to elide allocations. (Well this example may not make sense in Haskell because Haskell is lazily evaluated).

However there is a limit to what compiler can do, and it might manifest in edge cases like variation in order of imports. I'd rather have straightforward code than relying on compiler optimizations.

I am not arguing "against abstractions" like some Go fanboys tell you map and filter are less efficient. It is always possible to apply same map filter to iterators/lazy streams instead of arrays and get same performance in straightforward code. But that's not same as keeping in mind what heuristics compiler uses to optimize the code.

hopia6y ago

I suppose in FP/Haskell you would structure your code differently, so that it wouldn't have side effects when mapping arrays. That way you could even parallelize it trivially.

High level languages produce a lot less code than than less optimized implementations. Difficulties with reasoning about execution/performance is the penalty you potentially have to pay.

In my experience it indeed may be hard to understand performance with Haskell. That said, it comes with excellent tooling to overcome it in most of the cases.

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